1. Field of the Invention
This invention relates to a modified and improved heat pump or a retrofit alteration to an existing heat pump that enables the heat pump to increase its heating efficiency of an indoor space during cold outdoor conditions. A supplemental coil or heat exchanger system is provided that includes a control means for actively regulating within an efficient operating range the refrigerant suction pressure and temperature. As a direct result of the supplemental heat exchanger and the control means, additional heat may be drawn from outside air surrounding the main heat exchanger and supplemental heat exchanger units, thereby decreasing the need for expensive auxiliary resistance type heating strips.
2. Description of the Background Art
Devices relying upon standard heat pump technologies have been available for many years. Within the limits of each associated design specification, these devices enable a user to cool or heat a selected environment. For these heating and cooling duties, in general, gases or liquids are compressed, expanded, heated, or cooled within an essentially closed system to produce a desired temperature result in the selected environment. To accomplish the heating and cooling, heat is transferred from one location to another.
On days or evenings when the outside temperature nears or drops below freezing the efficiency of traditional heat pump systems drops off significantly. The subject apparatus and method of use overcomes this difficulty by enhancing, at low outside temperatures, the amount of expanded refrigerant that returns to the heat pump compressor, thereby increasing the efficiency of the heat exchange process by supplying additional heat containing refrigerant.
Concerning the existing prior references, specifically, U.S. Pat. No. 3,024,619 relates a heat pump system having an additional row of finned tubes on the outdoor heat exchanger. Due to a first associated check valve, the additional finned tubes act as a sub-cooler during a cooling cycle. When the system is run in reverse direction for heating, a second check valve passes coolant through the auxiliary coil thereby increasing heating capacity during the heating cycle without adversely affecting cooling operation. No direct monitoring coolant temperatures or pressures are associated with the regulation of this process.
A reverse cycle refrigeration system is disclosed in U.S. Pat. No. 3,365,902. The apparatus acts as a heat pump or as a system having a normal refrigeration phase and a hot gas defrost phase. A set of heat source coils forming a distinct refrigerant circuit is separate from the condenser coils but contained in a common fin bundle with the condenser coils.
U.S. Pat. No. 3,537,274 provides a dual evaporator refrigeration system. The system permits alternate connection of the evaporators for cooling while using the liquid refrigerant as the source of heat for defrosting the disconnected evaporator. There are two separate evaporators and a four-way valve for alternately connecting one or the other evaporator to the outlet side of the expansion device. The other evaporator is connected in the liquid refrigerant flow line so that liquid refrigerant passes through it. This liquid refrigerant serves as the source of heat for defrosting the evaporator not being used. As the four-way valve switches, the actions of the evaporators switch.
Disclosed in U.S. Pat. No. 3,918,268 is a heat pump with a frost-free outdoor coil. A heating means is associated with the normal outside coil to prevent the surface temperature of the outside coil from falling below 32.degree. C. Means are provided to prevent liquid floodback into the compressor when a changeover occurs from heating to cooling.
Described in U.S. Pat. No. 4,171,622 is a heat pump including an auxiliary outdoor heat exchanger acting as a defroster and sub-cooler. Located underneath the main outdoor heat exchanger and connected between the indoor and main outdoor heat exchangers is the auxiliary exchanger. During cooling the auxiliary exchanger acts as a sub-cooler and during heating it functions as a defroster for melting a block of ice that may have accumulated under or within the main outdoor heat exchanger.
U.S. Pat. No. 4,173,865 relates an auxiliary coil arrangement for a heat pump. The auxiliary coil is connected in parallel refrigerant flow arrangement with the expansion device of the heat pump. Standard check valves are provided to permit the auxiliary coil to function as a sub-cooler when the associated heat exchanger functions as a condenser.
Presented in U.S. Pat. No. 4,266,405 is a heat pump refrigerant circuit to reduce the time length of defrost cycles in contemporary air-to-air heat pumps. This reduction is accomplished by having two parallel refrigerant circuits connect the reversing valve to an outdoor coil. To regulate the direction of refrigerant flow, standard check valves are included.
A thermosyphon coil arrangement for a the outside unit of a heat pump is described in U.S. Pat. No. 4,449,377. When the heat pump is operating in the heating mode, the refrigerant flow is controlled by thermosyphoning action. Further, the coil placement and refrigerant flow are arranged for an outdoor unit so that the coil operates in an optimal thermosyphon fashion in the heating mode.
U.S. Pat. No. 4,553,401 discloses a reversible cycle heating and cooling system. Introduced is an auxiliary outdoor heat exchanger that is coupled with a water source for enhancing the capacity and efficiency of the system to transfer heat to the refrigerant during the heating mode at low outdoor ambient temperatures.
A capillary tube-type expansion device for a heat pump is explained in U.S. Pat. No. 4,563,879. To regulate the device, a control unit detects the temperature of the outside air and the discharge water temperature of a water-cooled heat exchanger and applies a suitable control signal to an electrical expansion valve.
An apparatus for enhancing the performance of a heat pump is given in U.S. Pat. No. 4,761,964. First and second auxiliary coils are heated with associated radiant quartz heating elements. Outdoor temperature is employed, via a pair of thermostats, to regulate the operation of the quartz heaters.
Provided in Japanese Patent No. 38,143 is a heat pump type system having first and second units. The amount of cooling medium is regulated to provide maximum heating and cooling capacity.